Central Lavas Research Articles

Discussion

Professor L. Hawkes welcomed the paper as marking a big advance in our understanding of the Tertiary igneous rocks of Iceland. To have been able to distinguish, in the pile of basic lavas, the flows of the central volcano from the fissure flood-basalts was a notable achievement. The general picture of volcanic activity the author had demonstrated was paralleled by that in central Iceland in historic times. Now that the field-relationships of the rocks had been elucidated it was to be hoped that a petrographical study would be made in the laboratory. The author attributed the thinness of the central lavas to flow on a slope. Did these lavas thicken on reaching the plain? Professor F. H. Stewart asked whether the author would say more about the nature of the gabbro and granophyre fragments in the agglomerates and about the rock referred to as representing an ‘emulsion’ of acid and basic magmas. Were any of the Icelandic volcanoes in this region eroded deeply enough to show ring-dykes or cone-sheets? Dr M.J. Le Bas expressed concern at Dr Walker’s use of the word <i>andesite.</i> The rocks so described did not appear to resemble to any great extent typical andesites such as were found in the orogens. Would not some other term, perhaps <i>trachybasalt,</i> be more appropriate for these Thulean rocks? Mr I. L. Gibson said that the author had convincingly demonstrated the interdigitation of the surrounding flood-basalts with the lavas of the flank of the volcano. Throughout the paper